Hairline cracks on the hood

BlueRooster · #1 (**permalink**) 09-13-2003, 06:40 PM

I have SPF 623 and I see hailline cracks developing near the hood scoop, and inside the hood towards the front. Is this typical? Is it from engine vibration? Keeping the hood open too long? I noticed the inside cracks after I had the car dynoed. This was performed with the hood open obviously. How can I repair this? Any easy fixes without major surgury?

KobraKarl · #2 (**permalink**) 09-13-2003, 06:58 PM

BR,

are you sure you are not looking at paint cracks ?

KK

427sharpe · #3 (**permalink**) 09-13-2003, 08:32 PM

These sound like they may be stress cracks developing in the 'glass....not a good thing. Is the hood a flush fit to the body (closed) or do you have to push a little to get the hood handles to close? How is the hood supported? I have seen a few cars develop cracks when using one of the gas struts to hold it open that are too strong or improperly mounted, which leaves a lot of stress on the hood, especially when closed. Can you post some pics, so we can see what kind of cracks you are talking about? They may give a few more clues about a fix.

Turk · #4 (**permalink**) 09-13-2003, 08:57 PM

The hood scoop is NOT touching the air cleaner while it is running, is IT?
If it barely clears the hood scoop it may be hitting against it due to torque.

TURK

Double Venom · #5 (**permalink**) 09-13-2003, 09:27 PM

Simple fix for any qualified fiberglas repair shop...But Turk and Sharpe are both right in thier own way. (Ouch that hurt to admit that!

The repair is fairly simple, it's that cause that may be a problem. First time I have ever heard of an SPF scoop cracking.

DV...an old, tired deFective. Bring it over, we'll fix it and find the cause

CRZN427 · #6 (**permalink**) 09-14-2003, 12:29 AM

Stress cracks sounds like the correct diagonosis.

A bad paint job, too thick, might also be what is seen.

Stress cracks can be caused by the things that were mentioned earlier but my theory is that they are due to internal stresses from the fiberglass curing at different rates for the thicker areas around the scoop, or due to the hole for the scoop opening causing the glass to shrink around the hole at a slightly different rate.

Fiberglass, like concrete, never stops curing. It is 99 and 99/100% cured in an hour, but that last tick takes a long time and, in my humble opinion, causes the internal stressing leading to the "stress cracks".

Some of it may be due to workmanship in not having perfectly uniform layers of cloth, during the layup, or from the resin/catilist mixture being slightly varied fom the start to the finish of a panel causing different cure rates (times) in one area.

The only cure I know of is to sand (grind) them out and fill the area with compatable material, cure it properly, and re paint.

Paint and body professionals may have a different suggestion.

427Aggie · #7 (**permalink**) 09-14-2003, 09:06 AM

On the early SPF cars they had normal thickness fiberglass on the scoop where it attached to the hood. We have had several around here. The wind causes the scoop to pull on the hood which causes the cracks. The newer cars has a thicker attachment to the hood so it doesn't do this.

Not sure of the way to fix it but I believe its pretty common. You might want to post over at the SPF chat site and you should get plenty of information on solutions.

Matt

Dream Master · #8 (**permalink**) 09-15-2003, 02:11 PM

Have you thought of contacting a SPF dealer? I for one have never seen any SPF cars with cracks in any fiberglass, and I am a Superformance dealer that has seen hundreds. Sorry, I did see one once that had been in an accident and repaired improperly.

Definately not Stress cracks, as the hood is not connected to the frame in any way and only floats on latches and rubber snubbers...so where would we find stress? Lets face it guys we never even found stress cracks in those vettes that were know for stress cracks, their stress cracks were always betwen the hood opening and the headlamp opening, which made perfect sense as the body torqed.

That older car number tells me that it has been out there for at least a few years, since we are now on car number 1800+. Seems strange that it had not surfaced earlier. Are you the original owner? Has it been repaired or repainted before? Sounds more like a film thickness issue with too much paint applied.

I am not sure what Matt is referring to as normal thickness, but none of our cars has had any problem with the thickness of fiberglass and cracking. I have deal with two that had a seperated under the hood area and showed up as a crack where bonding of the inner panel on the hood was. Easy fix.

Doug Reed

CRZN427 · #9 (**permalink**) 09-16-2003, 11:13 PM

I'll start off by admitting that I am no expert.

There are at least two ways to "stress the fiberglass".

One:

Attach a piece of fiberglass to something, and then bend that something so that the fiberglass is being forced into a different shape.

This can be from the weight of the body pushing down on the frame attachment points or from the hood and trunk area where the popular struts are used to lift and hold the hood and/or trunk open.

Even when the hood and/or trunk is closed the strut is applying force to the brackets and eventually, on most installations, to the fiberglass. This is introducing stress into the fiberglass.

Another way:

Build up the fiberglass in layers, sound familar, and have some differences in the resin mixture, the cure temperature, the thickness of the build up or possibly items that are embedded in the fibergalss such as hood, trunk and door mount nuts or bolts.

If the outer layers of fiberglass are cured at a different rate, or with a different resin minture, than the inner layers, there will be stress within the fiberglass generated by the two bonded surfaces trying to settle in their own shape.

The net effect is similar to the bi-metalic strips that are used in thermometers, where a change in temperature causes one of the strips to change length at a different rate than the other srtip and the bi-metalic unit curls to drive the gage pointer.

If you prevent the bi-metalic strip from bending, the two layers will be under some stress and it will likely show up as small wrinkles in the surface and/or cracks on the surface of one of the materials, probably the one being stretched.

This kind of stress is internal and will not be significanlty effected by how the body is mounted. Applying resin over the area, by sanding out the cracks and adding more material, may cure the problem and it may just start the process over again when the fresh resin cures on the existing panel.

There must be a fiberglass expert out there who has had experience in this area and can provide some useful advice.